The command set consists of a series of short text strings which can be combined to produce commands for operations such as dialing, hanging up, and changing the parameters of the connection. The vast majority of dial-up modems use the Hayes command set in numerous variations.

The command set covered only those operations supported by the earliest 300 bit/s modems. When new commands were required to control additional functionality in higher speed modems, a variety of one-off standards emerged from each of the major vendors. These continued to share the basic command structure and syntax, but added any number of new commands using some sort of prefix character – & for Hayes and USR, and \ for Microcom, for instance. Many of these re-standardized on the Hayes extensions after the introduction of the SupraFAXModem 14400 and the subsequent market consolidation that followed.

Prior to the introduction of the Bulletin Board System (BBS), modems typically operated on direct-dial telephone lines that always began and ended with a known modem at each end. The modems operated in either "originate" or "answer" modes, manually switching between two sets of frequencies for data transfer. Generally, the user placing the call would switch their modem to "originate" and then dial the number by hand. When the remote modem answered, already set to "answer" mode, the telephone handset was switched off and communications continued until the caller manually disconnected.

When automation was required, it was commonly only needed on the answer side — for instance, a bank might need to take calls from a number of branch offices for end-of-day processing. To fill this role, some modems included the ability to pick up the phone automatically when it was in answer mode, and clearing the line when the other user manually disconnected. The need for automated outbound dialling was considerably less common, and handled through a separate peripheral device, a "dialler". This was normally plugged into a separate input/output port on the computer (typically an RS-232 port) and programmed separately from the modem itself.

This method of operation worked satisfactorily in the 1960s and early 1970s, when modems were generally used to connect dumb devices like computer terminals (dialling out) with smart mainframe computers (answering). However, the microcomputer revolution of the 1970s led to the introduction of low-cost modems and the idea of a semi-dedicated point-to-point link was no longer appropriate. There were potentially thousands of users who might want to dial any of the other thousands of users, and the only solution at the time was to make the user dial manually.

The computer industry needed a way to tell the modem what number to dial through software. The earlier separate dialers had this capability, but only at the cost of a separate port, which a microcomputer might not have available. Another solution would have been to use a separate set of "command pins" dedicated to sending and receiving commands, another could have used a signal pin indicating that the modem should interpret incoming data as a command. Both of these had hardware support in the RS-232 standard. However, many implementations of the RS-232 port on microcomputers were extremely basic, and some eliminated many of these pins as a cost saving measure.

Hayes Communications introduced a solution in its 1981 Smartmodem by re-using the existing data pins with no modification. Instead, the modem itself could switch itself between one of two modes:

data mode in which the modem sends the data to the remote modem. (A modem in data mode treats everything it receives from the computer as data and sends it across the phone line).

command mode in which data is interpreted as commands to the local modem (commands that the local modem should execute).

To switch from data mode to command mode, sessions sent an escape sequence string of three plus signs ("+++") followed by a pause of about a second. The pause at the end of the escape sequence was required to reduce the problem caused by in-band signaling: if any other data was received within one second of the three plus signs, it was not the escape sequence and would be sent as data. To switch back they sent the online command, O. In actual use many of the commands automatically switched to the online mode after completion, and it is rare for a user to use the online command explicitly.

In order to avoid licensing Hayes's patent, some manufacturers implemented the escape sequence without the time guard interval (Time Independent Escape Sequence (TIES)). This had a major denial of service security implication in that it would lead to the modem hanging up the connection should the computer ever try to transmit the byte sequence "+++ATH0" in data mode. For any computer connected to the Internet through such a modem, this could be easily exploited by sending it a ping of death request containing the sequence "+++ATH0" in the payload. The computer operating system would automatically try to reply the sender with the same payload, immediately disconnecting itself from the Internet, as the modem would interpret the ICMP packet's data payload as a Hayes command.[2] The same error would also trigger if, for example, the user of the computer ever tried to send an e-mail containing the aforementioned string.

The Hayes command set includes commands for various phone-line manipulations, dialing and hanging-up for instance. It also includes various controls to set up the modem, including a set of register commands which allowed the user to directly set the various memory locations in the original Hayes modem. The command set was copied largely verbatim, including the meaning of the registers, by almost all early 300 baud modem manufacturers, of which there were quite a few.

The expansion to 1200 and 2400 baud required the addition of a small set of new commands, some of them prefixed with an ampersand ("&") to denote those dedicated to new functionality. Hayes itself was forced to quickly introduce a 2400 baud model shortly after their 1200, and the command sets were identical as a time-saving method.[3] Essentially by accident, this allowed users of existing 1200 baud modems to use the new Hayes 2400 models without changing their software. This re-inforced the use of the Hayes versions of these commands. Years later, the Telecommunications Industry Association (TIA)/Electronic Industries Alliance (EIA) raised the 2400-baud command set into a formal standard with the title Data Transmission Systems and Equipment - Serial Asynchronous Automatic Dialing and Control, TIA/EIA-602.

However, Hayes Communications moved only slowly to higher speeds or the use of compression, and three other companies led the way here — Microcom, U.S. Robotics and Telebit. Each of these three used its own additional command-sets instead of waiting for Hayes to lead the way. By the early-1990s, there were four major command sets in use, and a number of versions based on one of these. Things became simpler again during the widespread introduction of 14.4 and 28.8 kbit/s modems in the early 1990s. Slowly, a set of commands based heavily on the original Hayes extended set using "&" commands became popular, and then universal. Only one other command set has remained popular, the US Robotics set from their popular line of modems.

The following text lists part of the Hayes command set (also called the AT commands: "AT" meaning 'attention').

The Hayes command set can subdivide into four groups:

basic command set – A capital character followed by a digit. For example, M1.

extended command set – An "&" (ampersand) and a capital character followed by a digit. This extends the basic command set. For example, &M1. Note that M1 is different from &M1.

proprietary command set – Usually starting either with a backslash (“\”) or with a percent sign (“%”); these commands vary widely among modem manufacturers.

register commands – Sr=n where r is the number of the register to be changed, and n is the new value that is assigned.

A register represents a specific physical location in memory. Modems have small amounts of memory on board. The fourth set of commands serves for entering values into a particular register (memory location). The register will store a particular value (alpha-numeric information) which the modem and the communications software can utilize. For example, S7=60 instructs the modem to "Set register #7 to the value 60".

Although the command-set syntax defines most commands by a letter-number combination (L0, L1 etc.), the use of a zero is optional. In this example, "L0" equates to a plain "L". Keep this in mind when reading the table below.

When in data mode, an escape sequence can return the modem to command mode. The normal escape sequence is three plus signs ("+++"), and to disambiguate it from possible real data, a guard timer is used: it must be preceded by a pause, not have any pauses between the plus signs, and be followed by a pause; by default, a "pause" is one second and "no pause" is anything less.

<CR> Carriage return character, is the command line and result code terminator character, which value, in decimal ASCII between 0 and 255, is specified in register S3. The default value is 13.

<LF> Linefeed character, is the character recognised as line feed character. Its value, in decimal ASCII between 0 and 255, is specified in register S4. The default value is 10. The line feed character is output after the carriage return character if verbose result codes are used (V1 option is used); otherwise, if numeric format result codes are used (V0 option is used), it will not appear in the result codes.

<...> Name enclosed in angle brackets is a syntactical element. They do not appear in the command line.

[...] Optional subparameter of a command or an optional part of AT information response is enclosed in square brackets. Brackets themselves do not appear in the command line. When the subparameter is not given in AT commands which have a Read command, the new value equals its previous value. In AT commands which do not store the values of any of their subparameters, and so have not a Read command, which are called action type commands, the action should be done on the basis of the recommended default setting of the subparameter.

A string can contain many Hayes commands placed together, so as to optimally prepare the modem to dial out or answer, e.g. AT&F&D2&C1S0=0X4. This is called the initialization string.[5] The V.250 specification requires all DCEs to accept a body (after "AT") of at least 40 characters of concatenated commands.[6]

The following represents two computers, computer A and computer B, both with modems attached, and the user controlling the modems with terminal-emulator software. Terminal-emulator software typically allows the user to send Hayes commands directly to the modem, and to see the responses. In this example, the user of computer A makes the modem dial the phone number of modem B at phone number 555-1234 (long distance). After every command and response, there is a carriage return sent to complete the command.

Modem A

Modem B

Comment

ATDT15551234

User at modem A issues a dial command: AT-Get the modem's ATtention; D-Dial; T-Touch-Tone; 15551234-Call this number

The modems connect, and both modems report "connect". (In practice, most modems report more information after the word CONNECT — specifying the speed of the connection.) Also, at this time, both modems will raise the DCD, or Data Carrier Detect signal, on the serial port.

abcdef

abcdef

When the modems are connected, any characters typed at either side will appear on the other side. The person at computer A starts typing. The characters pass through the modem and appear on computer B's screen. (User A may not see his own typed characters — depending on the terminal software's local echo setting).

+++

The person at computer B issues the modem escape command. (Alternately, and more commonly, the computer B could drop the DTR, or Data Terminal Ready signal, to achieve a hangup, without needing to use +++ or ATH.)

OK

The modem acknowledges it.

ATH

The person at computer B issues a hang up command.

NO CARRIER

OK

Both modems report that the connection has ended. Modem B responds "OK" as the expected result of the command; modem A says NO CARRIER to report that the remote side interrupted the connection. The modems on both sides drop their DCD signals as well.

While the original Hayes command set represented a huge leap forward in modem-based communications, with time many problems set in, almost none of them due to Hayes per se:

Due to the lack of a written standard, other modem manufacturers just copied the external visible commands and (roughly) the basic actions. This led to a wide variety of subtle differences in how modems changed from state to state, and how they handled error conditions, hangups, and timeouts.

Each manufacturer tended to add new commands to handle emerging needs, often incompatible with other modems. For example, setting up hardware or software handshaking often required many different commands for different modems. This undermined the handy universality of the basic Hayes command set.

Many Hayes compatible modems had serious quirks that made them effectively incompatible. For example, many modems required a pause of several seconds after receiving the "AT Z" reset command. Some modems required spaces between commands, while others did not. Some would unhelpfully change baud-rate of their own volition, which would leave the computer with no clue how to handle the incoming data.

As a result of all this, eventually many communications programs had to give up any sense of being able to talk to all "Hayes-compatible" modems, and instead the programs had to try to determine the modem type from its responses, or provide the user with some option whereby they could enter whatever special commands it took to coerce their particular modem into acting properly.

The Hayes command set facilitated automatic baud rate detection as "A" and "T" happen to have bit patterns that are very regular; "A" is "100 0001" and so has a 1 bit at the start and end and "T" is "101 0100" which has a pattern with (nearly) every other bit set.[7] Since the RS-232 interface transmits least significant bit first, the according line pattern with 8-N-1 (eight data bits, no parity bit, one stop bit) is 11000001011001010101 (start and stop bits italicized) which is used as syncword.

The following commands are understood by virtually all modems supporting an AT command set, whether old or new.

Command

Description

Comments

A0 or A

Answer incoming call

A/

Repeat last command

Do not preface with AT, do not follow with carriage return. Enter usually aborts.

D

Dial

Dial the following number and then handshake

P - Pulse Dial
T - Touch Tone Dial
W - Wait for the second dial tone
R - Reverse to answer-mode after dialing
@ - Wait for up to 30 seconds for one or more ringbacks
, - Pause for the time specified in register S8 (usually 2 seconds)
; - Remain in command mode after dialing.
! - Flash switch-hook (Hang up for a half second, as in transferring a call.)
L - Dial last number

E0 or E

No Echo

Will not echo commands to the computer

E1

Echo

Will echo commands to the computer (so one can see what one types)

H0 or H

Hook Status

On hook. Hangs up the phone, ending any call in progress.

H1

Hook status

Off hook. Picks up the phone line (typically you'll hear a dialtone)

I0 to I9

Inquiry, Information, or Interrogation

This command returns information about the model, such as its firmware or brand name. Each number (0 to 9, and sometimes 10 and above) returns one line of modem-specific information, or the word ERROR if the line is not defined. Today, Windows uses this for Plug-and-play detection of specific modem types.

L0 or Ln (n=1 to 3)

Speaker Loudness. Supported only by some modems, usually external ones. Modems lacking speakers, or with physical volume controls, or ones whose sound output is piped through the sound card will not support this command.

Off or low volume

M0 or M

Speaker off, completely silent during dialing

M3 is also common, but different on many brands

M1

Speaker on until remote carrier detected (i.e. until the other modem is heard)

M2

Speaker always on (data sounds are heard after CONNECT)

O

Return Online

Returns the modem back to the normal connected state after being interrupted by the "+++" escape code.

Q0 or Q

Quiet Mode

Off - Displays result codes, user sees command responses (e.g. OK)

Q1

Quiet Mode

On - Result codes are suppressed, user does not see responses.

Sn

Select current register

Note that Sn, ? and =r are actually three separate commands, and can be given in separate AT commands.

Select register n as the current register

Sn?

Select register n as the current register, and query its value. Using ? on its own will query whichever register was most recently selected.

Sn=r

Select register n as the current register, and store r in it. Using =r on its own will store into whichever register was most recently selected.

Reset modem to stored configuration. Use Z0, Z1etc. for multiple profiles. This is the same as &F for factory default on modems without NVRAM (non volatile memory)

Note: a command string is terminated with a CR (\r) character

Although not part of the command set, a tilde character ~ is commonly used in modem command sequences. The ~ causes many applications to pause sending the command stream to the device (usually for half a second), e.g. after a Reset. The ~ is not sent to the modem.[8]

The ITU-T established a standard in its V-Series Recommendations, V.25 ter, in 1995 in an attempt to establish a standard for the command set again. It was renamed V.250 in 1998 with an annex that was not concerning the Hayes command set renamed as V.251. A V.250 compliant modem implements the A, D, E, H, I, L, M, N, O, P, Q, T, V, X, Z, &C, &D, and &F commands in the way specified by the standard. It must also implement S registers and must use registers S0, S3, S4, S5, S6, S7, S8, and S10 for the purposes given in the standard. It also must implement any command beginning with the plus sign, "+" followed by any letter A to Z, only in accordance with ITU recommendations. Modem manufacturers are free to implement other commands and S-registers as they see fit, and may add options to standard commands.

GSM/3G modems typically support the ETSI GSM 07.07/3GPP TS 27.007 AT command set extensions, although how many commands are implemented varies.

Most USB modem vendors, such as Huawei, Sierra Wireless, Option, have also defined proprietary extensions for radio mode selection (GSM/3G preference) or similar. Some recent high speed modems provide a virtual Ethernet interface instead of using a Point-to-Point Protocol (PPP) for the data connection because of performance reasons (PPP connection is only used between the computer and the modem, not over network). The set-up requires vendor-specific AT command extensions. Sometimes the specifications for these extensions are openly available, other times the vendor requires an NDA for access to these.[11]

1.
Modem
–
A modem is a network hardware device that modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information. The goal is attempting to produce a signal that can be transmitted easily, modems can be used with any means of transmitting analog signals, from light emitting diodes to radio. Modems are generally classified by the amount of data they can send in a given unit of time, usually expressed in bits per second. Modems can also be classified by their rate, measured in baud. The baud unit denotes symbols per second, or the number of times per second the modem sends a new signal. For example, the ITU V.21 standard used audio frequency shift keying with two frequencies, corresponding to two distinct symbols, to carry 300 bits per second using 300 baud. By contrast, the original ITU V.22 standard, which could transmit and receive four distinct symbols, news wire services in the 1920s used multiplex devices that satisfied the definition of a modem. However, the function was incidental to the multiplexing function, so they are not commonly included in the history of modems. S. SAGE modems were described by AT&Ts Bell Labs as conforming to their newly published Bell 101 dataset standard, while they ran on dedicated telephone lines, the devices at each end were no different from commercial acoustically coupled Bell 101,110 baud modems. The 201A and 201B Data-Phones were synchronous modems using two-bit-per-baud phase-shift keying, the famous Bell 103A dataset standard was also introduced by AT&T in 1962. It provided full-duplex service at 300 bit/s over normal phone lines, frequency-shift keying was used, with the call originator transmitting at 1,070 or 1,270 Hz and the answering modem transmitting at 2,025 or 2,225 Hz. The readily available 103A2 gave an important boost to the use of remote low-speed terminals such as the Teletype Model 33 ASR and KSR, AT&T reduced modem costs by introducing the originate-only 113D and the answer-only 113B/C modems. For many years, the Bell System maintained a monopoly on the use of its phone lines, however, the seminal Hush-a-Phone v. FCC case of 1956 concluded it was within the FCCs jurisdiction to regulate the operation of the Bell System. The FCC found that as long as a device was not electronically attached to the system and this led to a number of devices that mechanically connected to the phone through a standard handset. Since most handsets were supplied by Western Electric and thus of a standard design and this type of connection was used for many devices, such as answering machines. Acoustically coupled Bell 103A-compatible 300 bit/s modems were common during the 1970s, well-known models included the Novation CAT and the Anderson-Jacobson, the latter spun off from an in-house project at Stanford Research Institute. An even lower-cost option was the Pennywhistle modem, designed to be built using parts from electronics scrap, in December 1972, Vadic introduced the VA3400, notable for full-duplex operation at 1,200 bit/s over the phone network. Like the 103A, it used different frequency bands for transmit, in November 1976, AT&T introduced the 212A modem to compete with Vadic

2.
Computer terminal
–
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. The function of a terminal is confined to display and input of data, a terminal that depends on the host computer for its processing power is called a dumb terminal or thin client. A personal computer can run terminal emulator software that replicates the function of a terminal, sometimes allowing concurrent use of local programs and access to a distant terminal host system. The terminal of the first working programmable, fully automatic digital Turing-complete computer, the Z3, had a keyboard, early user terminals connected to computers were electromechanical teleprinters/teletypewriters, such as the Teletype Model 33 ASR, originally used for telegraphy or the Friden Flexowriter. Later printing terminals such as the DECwriter LA30 were developed, however printing terminals were limited by the speed at which paper could be printed, and for interactive use the paper record was unnecessary. The problem was that the amount of memory needed to store the information on a page of text was comparable to the memory in low end minicomputers then in use. Displaying the information at video speeds was also a challenge and the control logic took up a rack worth of pre-integrated circuit electronics. Another approach involved the use of the tube, a specialized CRT developed by Tektronix that retained information written on it without the need to refresh. The Datapoint 3300 from Computer Terminal Corporation was announced in 1967 and shipped in 1969 and it solved the memory space issue mentioned above by using a digital shift-register design, and using only 72 columns rather than the later more common choice of 80. Some type of blinking cursor that can be positioned, the term intelligent in this context dates from 1969. Notable examples include the IBM2250 and IBM2260, predecessors to the IBM3270, providing even more processing possibilities, workstations like the Televideo TS-800 could run CP/M-86, blurring the distinction between terminal and Personal Computer. Most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen, typically terminals communicate with the computer via a serial port via a null modem cable, often using an EIA RS-232 or RS-422 or RS-423 or a current loop serial interface. In fact, the design for the Intel 8008 was originally conceived at Computer Terminal Corporation as the processor for the Datapoint 2200. While early IBM PCs had single color green screens, these screens were not terminals. The screen of a PC did not contain any character generation hardware, all signals and video formatting were generated by the video display card in the PC, or by the CPU. An IBM PC monitor, whether it was the monochrome display or the 16-color display, was technically much more similar to an analog TV set than to a terminal. With suitable software a PC could, however, emulate a terminal, the Data General One could be booted into terminal emulator mode from its ROM. Since the advent and subsequent popularization of the computer, few genuine hardware terminals are used to interface with computers today

3.
Microcomputer revolution
–
Prior to 1977, the only contact most of the population had with computers was through utility bills, bank and payroll services, or computer-generated junk mail. Within a decade, computers became common consumer goods, the advent of affordable personal computers has had lasting impact on education, business, music, social interaction, and entertainment. The minicomputer ancestors of the personal computer used early integrated circuit technology, which reduced size and cost. This meant that they were large and difficult to manufacture just like their mainframe predecessors. After the computer-on-a-chip was commercialized, the cost to manufacture a computer system dropped dramatically, the arithmetic, logic, and control functions that previously occupied several costly circuit boards were now available in one integrated circuit, making it possible to produce them in high volume. Concurrently, advances in the development of solid state memory eliminated the bulky, costly, after the 1971 introduction of the Intel 4004, microprocessor costs declined rapidly. In 1974 the American electronics magazine Radio-Electronics described the Mark-8 computer kit, in January of the following year, Popular Electronics magazine published an article describing a kit based on the Intel 8080, a somewhat more powerful and easier to use processor. The Altair 8800 sold remarkably well even though initial memory size was limited to a few hundred bytes, expansion memory boards and peripherals were soon listed by the original manufacturer, and later by plug compatible manufacturers. The very first Microsoft product was a 4 kilobyte paper tape BASIC interpreter, the alternative was to hand-assemble machine code that could be directly loaded into the microcomputers memory using a front panel of toggle switches, pushbuttons and LED displays. Children would use disk-based encyclopedias for school work and would be avid video gamers, home automation would bring about the intelligent home of the 1980s. Using Videotex, NAPLPS or some sort of as-yet unrealized computer technology, the personalized newspaper was a commonly predicted application. Morning coffee would be brewed automatically under computer control, the same computer would control the house lighting and temperature. Robots would take the garbage out, and be programmable to perform new tasks by the home computer, all this was predicted to be commonplace sometime before the end of the decade, but virtually every aspect of the predicted revolution would be delayed or prove entirely impractical. The computers available to consumers of the period just werent powerful enough to perform any single task required to realize this vision. The home computers of the early 1980s could not multitask, before long, a backlash set in—computer users were geeks, nerds or worse, hackers. The North American video game crash of 1983 soured many on home computer technology, predicted aspects of the revolution were left by the wayside or modified in the face of an emerging reality. The cost of electronics dropped precipitously and today many families have a computer for each family member, encyclopedias, recipe catalogs and medical databases are kept online and accessed over the world wide web not stored locally on floppy disks or CD-ROM. Our coffee may be brewed automatically every morning, but the computer is a simple one embedded in the coffee maker, as of 2008, robots are just beginning to make an impact in the home, with Roomba and Aibo leading the charge

4.
Plug and play
–
Plug and play devices can be due to boot-time assignment of device resources and to hotplug systems such as USB and IEEE1394. In the beginnings of data processing technology, the hardware was just a collection of modules, and this linking was usually done by connecting some wires between modules and disconnecting others. Some early microcomputing devices such as the Apple II sometimes required the end-user to physically cut some wires, the changes were intended to be largely permanent for the life of the hardware. As computers became more accessible to the public, the need developed for more frequent changes to be made by computer users unskilled with using soldering irons. Rather than cutting and soldering connections, configuration was accomplished by jumpers or DIP switches, however, the process of configuring devices manually using jumpers or DIP switches, could be quite difficult, and there was usually no forgiveness for technical inexperience. Incorrect settings could render either the system or just the expansion device completely or partially inoperable. The system might still have seemed to work properly with a setting, until the IRQ or DMA was actually needed. No jumpers or any manual configuration was required, and the independent address space for each slot allowed very cheap & commonplace chips to be used, alongside with cheap glue logic. On the software site, the drivers and extensions were supplied in the cards own ROM, the ROM extensions abstracted any hardware differences and offered standard APIs as specified by ASCII Corporation. In 1984, the NuBus architecture was developed by the Massachusetts Institute of Technology as a platform agnostic peripheral interface that fully automated device configuration, the specification was sufficiently intelligent that it could work with both big endian and little endian computer platforms that had previously been mutually incompatible. However, this agnostic approach increased interfacing complexity and required support chips on every device which in the 1980s was expensive to do, in 1984, Commodore developed the AutoConfig protocol and the Zorro expansion bus for its Amiga line of expandable computers. The first public appearance was in the CES computer show at Las Vegas in 1985, like NuBus, Zorro devices had absolutely no jumpers or DIP switches. The Zorro architecture did not spread to general computing use outside of the Amiga product line, in 1987, IBM released an update to the IBM PC known as the Personal System/2 line of computers using the Micro Channel Architecture. The PS/2 was capable of totally automatic self-configuration, every piece of expansion hardware was issued with a floppy disk containing a special file used to auto-configure the hardware to work with the computer. The user would install the device, turn on the computer, load the configuration information from the disk, and the hardware automatically assigned interrupts, DMA, and so forth. However, the disks posed a problem if they were damaged or lost, without the disks, any new hardware would be completely useless and the computer would not boot at all until the unconfigured device was removed. Microchannel did not gain support, because IBM wanted to exclude clone manufacturers from this next generation computing platform. Anyone developing for MCA had to sign agreements and pay royalties to IBM for each device sold

5.
Fax
–
Fax, sometimes called telecopying or telefax, is the telephonic transmission of scanned printed material, normally to a telephone number connected to a printer or other output device. The receiving fax machine interprets the tones and reconstructs the image, early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines modulate the audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black. Scottish inventor Alexander Bain worked on chemical mechanical fax type devices and he received British patent 9745 on May 27,1843 for his Electric Printing Telegraph. Frederick Bakewell made several improvements on Bains design and demonstrated a telefax machine, the Pantelegraph was invented by the Italian physicist Giovanni Caselli. He introduced the first commercial service between Paris and Lyon in 1865, some 11 years before the invention of the telephone. In 1880, English inventor Shelford Bidwell constructed the scanning phototelegraph that was the first telefax machine to scan any two-dimensional original, previously, photographs had been sent over the radio using this process. The Western Union Deskfax fax machine, announced in 1948, was a machine that fit comfortably on a desktop. As a designer for the Radio Corporation of America, in 1924, Richard H. Ranger invented the wireless photoradiogram, or transoceanic radio facsimile, the forerunner of today’s fax machines. A photograph of President Calvin Coolidge sent from New York to London on November 29,1924 became the first photo picture reproduced by transoceanic radio facsimile, commercial use of Ranger’s product began two years later. Also in 1924, Herbert E. Ives of AT&T Corporation transmitted and reconstructed the first color facsimile, around 1952 or so, Finch Facsimile, a highly developed machine, was described in detail in a book, it was never manufactured in quantity. By the late 1940s, radiofax receivers were sufficiently miniaturized to be fitted beneath the dashboard of Western Unions Telecar telegram delivery vehicles, in the 1960s, the United States Army transmitted the first photograph via satellite facsimile to Puerto Rico from the Deal Test Site using the Courier satellite. Radio fax is still in limited use today for transmitting weather charts, in 1964, Xerox Corporation introduced what many consider to be the first commercialized version of the modern fax machine, under the name or Long Distance Xerography. This model was superseded two years later with a unit that would set the standard for fax machines for years to come. Up until this point facsimile machines were expensive and hard to operate. In 1966, Xerox released the Magnafax Telecopiers, a smaller and this unit was far easier to operate and could be connected to any standard telephone line. This machine was capable of transmitting a letter-sized document in about six minutes, the first sub-minute, digital fax machine was developed by Dacom, which built on digital data compression technology originally developed at Lockheed for satellite communication. By the late 1970s, many companies around the world, entered the fax market, very shortly after a new wave of more compact, faster and efficient fax machines would hit the market

6.
Bulletin board system
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A bulletin board system, or BBS, is a computer server running software that allows users to connect to the system using a terminal program. Many BBSes also offer on-line games, in users can compete with each other. Bulletin board systems were in many ways a precursor to the form of the World Wide Web, social networks. Low-cost, high-performance modems drove the use of services and BBSes through the early 1990s. Infoworld estimated there were 60,000 BBSes serving 17 million users in the United States alone in 1994, over the next year, many of the leading BBS software providers went bankrupt and tens of thousands of BBSes disappeared. Today, BBSing survives largely as a hobby in most parts of the world. Most BBSes are now accessible over Telnet and typically offer free email accounts, FTP services, IRC, some offer access through packet switched networks, or packet radio connections. A precursor to the bulletin board system was Community Memory, started in August 1973 in Berkeley. Useful microcomputers did not exist at that time, and modems were both expensive and slow, Community Memory therefore ran on a mainframe computer and was accessed through terminals located in several San Francisco Bay Area neighborhoods. The poor quality of the original modem connecting the terminals to the mainframe prompted a user to invent the Pennywhistle modem, Community Memory allowed the user to type messages into a computer terminal after inserting a coin, and offered a pure bulletin board experience with public messages only. It did offer the ability to tag messages with keywords, which the user could use in searches, the system acted primarily in the form of a buy and sell system with the tags taking the place of the more traditional classifications. But users found ways to express themselves outside these bounds, unfortunately, the system was expensive to operate, and when their host machine became unavailable and a new one could not be found, the system closed in January 1975. Similar functionality was available to most mainframe users, which might be considered a sort of ultra-local BBS when used in this fashion. Commercial systems, expressly intended to offer features to the public, became available in the late 1970s. Early modems were very simple devices using acoustic couplers to handle telephone operation. The user would first pick up the phone, dial a number, disconnecting at the end of a call required the user to pick up the handset and return it to the phone. With the introduction of microcomputers with expansion slots, like the S-100 bus machines and Apple II, it possible for the modem to communicate instructions. A number of modems of this sort were available by the late 1970s

7.
USRobotics
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U. S. Robotics Corporation, often called USR, is a company that produces USRobotics computer modems and related products. Its initial marketing was aimed at bulletin board systems, where its high-speed HST protocol made FidoNet transfers much faster, during the 1990s it became a major consumer brand with its Sportster line. The company had a reputation for quality and support for the latest communications standards as they emerged, notably in its V. Everything line. With the reduced usage of analog or voiceband modems in North America in the early 21st century, the company purchased Palm, Inc. for its PalmPilot PDA, but was itself purchased by 3Com soon after. 3Com spun off USR again in 2000, keeping Palm and returning USR to the now much smaller modem market, after 2004 the company is formally known as USR. It is one of the few left in the modem market today. The company name is a reference to the fiction of Isaac Asimov, asimovs robot stories featured a fictional company named U. S. Cowell stated at a popular BBS convention they named the company as an homage to Asimov, robots eventually became the biggest company in the universe. USR was one of many companies to offer dial-up modems for personal computers, prior to the development of standards such as the V.32 family of protocols, USR introduced its own HST protocol in 1986, which operated at 9600 bit/s. In 1989 HST was expanded to 14.4 kbit/s,16.8 kbit/s in 1992, however, USR became the most successful of the three, due to a marketing scheme that offered large discounts to BBS sysops. The proprietary nature of HST allowed USR to maintain its market even when off-brand V. 32-based modems began selling for less than equivalent HST modems. As the price decreased, however, V. 32-based modems eventually became a cost-effective alternative to HST. The Sportster used the same motherboard as the Couriers, and on certain 14.4 kbit/s models a sequence of AT commands could be issued to enable the faster 16.8 kbit/s HST mode. The Courier modems remained a favorite in the BBS and emerging Internet service provider world, a similar situation emerged a few years later when the 56kbit/s V.90 standard was first being proposed. USR developed its own 56k standard known as X2, while a consortium of companies introduced its own K56flex. In contrast to the success of HST, neither X2 nor K56flex saw any real market uptake, after the introduction of V.90, USR abandoned support for X2. In a further effort to reduce the price of its modems. Some models of Courier modems were known for their long-term upgradeability, because they used an upgradeable DSP design

8.
SupraFAXModem 14400
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The SupraFAXModem 14400 was a v. 32bis modem. Launched in January 1992 at a price point, the 14,400 bit/s model was less expensive than most 9600 bit/s models, supported many additional features. Whereas a 9600 bit/s model was perhaps only a month before its introduction. Supra, Inc. had been a player in the computer market through the mid-to-late 1980s, known originally for their external hard drives for the Atari ST. During 1991, Rockwell Internationals chip-making arm developed a new modem driver chipset that included all of the latest standards that were then under development. Supra, never having been known as a player in the world, designed a modem based on the new chipset. Not content with simply being the first consumer v. 32bis modem on the market, one was the use of a much smaller case, about half the size of most models. The Supras smaller design made it easier to fit on a desk. Later models such as the LC used individual lamps that were a feature of external modems. In addition to the modem, Supra also introduced software to make better use of all the features of the modem. In particular, Supra re-packaged FAXstf as FAXCilitate, a Macintosh fax application that any application that supported printing to send the output as a fax instead. They later introduced Supra VoiceMail, another Mac application written by STF Technologies that turned the computer into a digital answering machine with caller id routing, the SupraFAXModem was by no means a perfect product. Both of these make them unsuitable for host side use on a bulletin board system or internet service provider. Supra also released a v.32 version at the same time, mentions of it disappear by late 1992. The 144LC was a Low-Cost version that lacked the alphanumeric display and they followed up the 14400s with the SupraFAXModem 288, the first consumer v.34 modem, and then a series of various versions with different features. The SupraExpress was a low-cost series that scaled to lower price points, housed in an all-plastic case, news/Networking, InfoWorld,10 February 1992, pg.53. SupraFAXModem, news release in the Atari SIG of the Cleveland Freenet

9.
Mainframe computer
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The term originally referred to the large cabinets called main frames that housed the central processing unit and main memory of early computers. Later, the term was used to distinguish high-end commercial machines from less powerful units, most large-scale computer system architectures were established in the 1960s, but continue to evolve. Their high stability and reliability enable these machines to run uninterrupted for decades, Mainframes are defined by high availability, one of the main reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic. The term reliability, availability and serviceability is a characteristic of mainframe computers. Proper planning and implementation is required to exploit these features, and if improperly implemented, in the late 1950s, most mainframes had no explicitly interactive interface, but only accepted sets of punched cards, paper tape, or magnetic tape to transfer data and programs. In cases where interactive terminals were supported, these were used almost exclusively for applications rather than program development, typewriter and Teletype devices were also common control consoles for system operators through the 1970s, although ultimately supplanted by keyboard/display devices. By the early 1970s, many mainframes acquired interactive user interfaces and operated as timesharing computers, users gained access through specialized terminals or, later, from personal computers equipped with terminal emulation software. By the 1980s, many mainframes supported graphical terminals, and terminal emulation and this format of end-user computing reached mainstream obsolescence in the 1990s due to the advent of personal computers provided with GUIs. After 2000, most modern mainframes have partially or entirely phased out classic green screen terminal access for end-users in favour of Web-style user interfaces, the infrastructure requirements were drastically reduced during the mid-1990s, when CMOS mainframe designs replaced the older bipolar technology. IBM claimed that its newer mainframes could reduce data center energy costs for power and cooling, modern mainframes can run multiple different instances of operating systems at the same time. This technique of virtual machines allows applications to run as if they were on physically distinct computers, in this role, a single mainframe can replace higher-functioning hardware services available to conventional servers. While mainframes pioneered this capability, virtualization is now available on most families of computer systems, Mainframes can add or hot swap system capacity without disrupting system function, with specificity and granularity to a level of sophistication not usually available with most server solutions. Modern mainframes, notably the IBM zSeries, System z9 and System z10 servers, such a two-mainframe installation can support continuous business service, avoiding both planned and unplanned outages. In practice many customers use multiple mainframes linked either by Parallel Sysplex and shared DASD, or with shared, Mainframes are designed to handle very high volume input and output and emphasize throughput computing. Since the late-1950s, mainframe designs have included subsidiary hardware which manage the I/O devices and it is common in mainframe shops to deal with massive databases and files. Gigabyte to terabyte-size record files are not unusual, compared to a typical PC, mainframes commonly have hundreds to thousands of times as much data storage online, and can access it reasonably quickly. Other server families also offload I/O processing and emphasize throughput computing, Mainframes also have execution integrity characteristics for fault tolerant computing. This hardware-level feature, also found in HPs NonStop systems, is known as lock-stepping, not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing

10.
Tilde
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The tilde is a grapheme with several uses. The name of the character came into English from Spanish, which in came from the Latin titulus. The reason for the name was that it was written over a letter as a scribal abbreviation, as a mark of suspension. Thus the commonly used words Anno Domini were frequently abbreviated to Ao Dñi, such a mark could denote the omission of one letter or several letters. This saved on the expense of the labour and the cost of vellum. Medieval European charters written in Latin are largely made up of such abbreviated words with suspension marks and other abbreviations, the tilde has since been applied to a number of other uses as a diacritic mark or a character in its own right. These are encoded in Unicode at U+0303 ◌̃ Combining Tilde and U+007E ~ Tilde, in lexicography, the latter kind of tilde and the swung dash are used in dictionaries to indicate the omission of the entry word. This symbol informally means approximately, about, or around, such as ~30 minutes before and it can mean similar to, including of the same order of magnitude as, such as, x ~ y meaning that x and y are of the same order of magnitude. The tilde is used to indicate equal to or approximately equal to by placing it over the = symbol, like so. The text of the Domesday Book of 1086, relating for example, the text with abbreviations expanded is as follows, Mollande tempore regis Edwardi geldabat pro iiii hidis et uno ferling. In dominio sunt iii carucae et x servi et xxx villani et xx bordarii cum xvi carucis, ibi xii acrae prati et xv acrae silvae. Pastura iii leugae in longitudine et latitudine, elwardus tenebat tempore regis Edwardi pro manerio et geldabat pro dimidia hida. Ibi sunt v villani cum i servo, valet xx solidos ad pensam et arsuram. Eidem manerio est injuste adjuncta Nimete et valet xv solidos, ipsi manerio pertinet tercius denarius de Hundredis Nortmoltone et Badentone et Brantone et tercium animal pasturae morarum. The incorporation of the tilde into ASCII is a result of its appearance as a distinct character on mechanical typewriters in the late nineteenth century. Any good typewriter store had a catalog of alternative keyboards that could be specified for machines ordered from the factory, at that time, the tilde was used only in Spanish and Portuguese typewriters. In Modern Spanish, the tilde is used only with n and N, both were conveniently assigned to a single mechanical typebar, which sacrificed a key that was felt to be less important, usually the 1⁄2— 1⁄4 key. Portuguese, however, uses not ñ but nh and it uses the tilde on the vowels a and o

11.
Telephone line
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A telephone line or telephone circuit is a single-user circuit on a telephone communication system. Telephone lines are used to deliver landline telephone service and Digital subscriber line phone service to the premises. Telephone overhead lines are connected to the switched telephone network. Modern lines may run underground, and may carry analog or digital signals to the exchange, often the customer end of that wire pair is connected to a data access arrangement, the telephone company end of that wire pair is connected to a telephone hybrid. In most cases, two wires for each telephone line run from a home or other small building to a local telephone exchange. The wires between the box and the exchange are known as the local loop, and the network of wires going to an exchange. The vast majority of houses in the U. S. are wired with 6-position modular jacks with four conductors wired to the junction box with copper wires. Those wires may be connected back to two telephone lines at the local telephone exchange, thus making those jacks RJ14 jacks. More often, only two of the wires are connected to the exchange as one line, and the others are unconnected. In that case, the jacks in the house are RJ11, inside the walls of the house—between the houses outside junction box and the interior wall jacks—the most common telephone cable in new houses is Category 5 cable—4 pairs of 24 AWG solid copper. Inside large buildings, and in the cables that run to the telephone company POP

12.
Hayes Microcomputer Products
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Hayes Microcomputer Products was a U. S. -based manufacturer of modems. This smart modem approach dramatically simplified and automated operation, today almost all modems use a variant of the Hayes command set. Hayes was a brand in the modem market from the introduction of the original 300 bit/s Smartmodem in 1981. They remained a major throughout the 1980s, periodically introducing models with higher throughput. In the early 1990s a number of greatly cost-reduced high-performance modems were released by competitors, notably the SupraFAXModem 14400, Hayes was never able to respond effectively. The widespread introduction of ADSL and cable modems in the mid-1990s repeatedly drove the company in Chapter 11 protection before being liquidated in 1999, dennis C. Hayes job was to set up modem connections for NDCs customers. The connection and disconnection was entirely manual, with the picking up the phones handset, dialing manually. Disconnecting at the end of the session was also manual, with the user lifting the handset out of the coupler and hanging it up on the phone body. There were optional systems to dial the phone or pick it up, such devices were typically expensive, and generally used by larger organizations like banks, who might use one to send an end-of-day file to branch offices. Hayes was a computer hobbyist, and felt that modems would be compelling to users of the new 8-bit computers that would soon be known as home computers. However, existing modems were simply too expensive and difficult to use or be practical for most users. What was needed was a single modem that could do it all, connect directly to the phone, answer incoming calls, dial numbers to initiate outgoing calls, the main problem with producing such a modem was forwarding commands from the computer. This could be addressed in internal modems that plugged directly into the computers motherboard and this was a straightforward and thus a popular solution, the Novation APPLE-CAT II for the Apple II computer was an early programmable modem of this type. Hayes started producing similar products at a level in his kitchen in April 1977 with his friend and co-worker. Their first product was the 80-103A, a 300 bit/s Bell 103-compatible design for S-100 bus machines, business picked up quickly, and in January 1978 they quit their jobs at National Data to form their own company, D. C. Hayes Associates. In 1980 the company changed its name to Hayes Microcomputer Products, although powerful, the internal modem was commercially impractical. Not only did it require special software, but a different hardware design was needed for every computer bus, including Apple II, S-100, TRS-80. Some popular computers, like the Atari 400, did not even integrate internal slots, an obvious solution was to use the RS-232 serial port, modems were serial devices and generally driven off RS-232 anyway, and most computer designs included an RS-232 port, or some variant

Diagrammatic oscilloscope trace of voltage levels for an ASCII "K" character (0x4B) with 1 start bit, 8 data bits, 1 stop bit. This is typical for start-stop communications, but the standard does not dictate a character format or bit order.